1. Field of the Invention
The invention relates to pulverulent olefin-maleic anhydride polymers which are produced from concentrated solutiosn of olefins and maleic anhydride in organic solvents, by radical polymerizaton.
2. Discussion of the Background
Olefins such as ethylene, propene, 1-butene, or isobutene can be copolymerized with maleic anhydride. This gives rise to copolymers with equimolar proportions of olefin and maleic anhyride.
When the polymerization is carried out in organic solvents, at temperatures above 100.degree. C., soft, adhesive products are produced which tend to clump together and stick to stirrers and reactor walls. High temperatures tend to promote formation of low molecular weight polymers, however. Such polymers may be used, for example, as dispersants.
At temperatures below 100.degree. C., pulverulent olefin-maleic anhydride copolymers can be prepared. However, a disadvantage is that at low temperatures very long reaction times are required for maleic anhydride conversions greater than 90%.
In known methods, an effort is made to reduce the molecular weight by adding various additives at low temperatures. These additives are, for example, carboxylic acids (British Patent No. 851,237), phosphites (U.S. Pat. No. 2,857,365), and aldehydes (U.S. Pat. No. 2,938,016). As a result, low molecular weight olefin-maleic anhydride copolymers are precipitated from organic solutions at 40.degree.-80.degree. C., and can be separated out. The reaction times are generally about 20 hr.
In all experiments, solids contents of not more than 20% are obtained at the conclusion of the polymerization.
According to Japanese Patent No. 54,156,092, olefins with preferably 4-6 carbon atoms can be copolymerized with maleic anhydride. Ethylene-vinyl acetate copolymer is added to diminish or eliminate adhesion of the polymer product to the reaction vessel. The polymerization is carried out in aliphatic hydrocarbons at 75.degree. C., in about 3 hr. Maleic anhydride conversions of 70-80% and solids contents of &lt;20% are obtained.
Industrially important maleic anhydride conversions are in the range &gt;90%, and industrially important solids contents are in the range &gt;20%. These are not described in Japanese Pat. No. 54-156,092.